1. Field of the Invention
The present invention relates to an alternating current (AC) signal producer, and in particular to an AC signal producer utilizing a Class-D technique for converting a direct current (DC) signal to an AC signal and a method thereof.
2. Description of Related Art
A power converter in a power supply for converting a power source is classified into different types, such as AC to AC, AC to DC, DC to AC, and DC to DC. In general, the power converter for a general consumer electronic product or an electronic car product may convert an AC input from a power source to a DC voltage signal so that the general consumer electronic product or the electronic car product could be powered. If the electronic product is driven by an AC voltage signal, the power supply needs to further convert the DC voltage signal into the AC voltage signal.
Many AC power supplies use a transformer to step up or step down the voltage signal. One of the advantages of this method is that the noise is separated from the input end of the AC power supplies. Another advantage is the elimination of the noise of the output end that influences the power source at the input end. Moreover, the power provided by the transformer is more than the active component.
Please refer to FIG. 1, which shows a schematic diagram of the conventional power source converting the DC signal to the AC signal. When a DC system 10 converts the DC signal to the AC signal for an AC system 13, the DC system 10 uses an oscillator circuit 11 to output AC signal. Next, a transformer 12 converts the AC signal to a voltage level required by the AC system 13. Therefore, the DC system 10 requires the transformer 12 and the oscillator circuit 11 to output the AC signal of the required voltage level for the AC system 13.
However, a structure using a transformer for converting the DC signal to the AC signal has some disadvantages, described in the below:                1. The efficiency of power conversion is at about 50 to 60%.        2. The inductance of the transformer changes depending on the changes in the temperature, which may affect the oscillating frequency of the oscillator or even cause the oscillator not to oscillate.        3. The transformer is expensive, driving up the cost of the structure.        4. The value of the inductance of the transformer can't be controlled accurately. Therefore, the quality of the transformer is unstable.        5. The size of the transformer is large.        